Hi Apple(of my eye 🙂
When you're entering a post / comment, the bar at the top of the box you're typing in has a number of 'icons' on it, the leftmost being the 'B' meaining Bold, followed by the I meaning Italic. If you go along to the right just after the smiley face is a piece of chain, and then a square box looking like a picture.
If you put your cursor on top of this square, without clicking it, it will display the words "Insert/Edit Image".
Click this button and another window will come up, with two tabs at the top. The left hand tab says "Add Image" and the right hand tab says "From My Uploaded Images". You need to click the left hand tab, then underneath the "Choose File" button you will see a blue line saying "From Another Site". Click this line and the window will change to have a text box with the label Image.
It's not a very big text box, but you can copy and paste the link (url) to your image into this text box. Be sure to give it a title, and probably choose the size Medium or Large.
Leave the Alignment at Inline.
After all is done, click the button at the bottom, labelled Insert Image.
Hope that helps!